Heat-curable aminoorganopolysiloxane compositions are described in U.S. Pat. No. 3,449,289 (hereinafter referred to as Schank et al.). The compositions disclosed in Schank et al. (hereinafter referred to as the "Schank et al. compositions") comprise
(a) an aminoorganopolysiloxane copolymer containing an average of at least 2 silicon-bonded groups represented by the formula --R.sup.1 NZ.sub.2 and consisting essentially of units of the formula: ##STR1## and units of the formula: ##STR2## wherein R is a monovalent hydrocarbon radical or a substituted monovalent hydrocarbon radical wherein the substituents are selected from the class consisting of fluoro substituents, cyano groups, alkoxy groups, polyoxyalkylene-substituted alkoxy groups, carbalkoxy groups and nitro groups; R.sup.1 is a divalent hydrocarbon group having at least three carbon atoms separating the [--NZ.sub.2 ] group from silicon; Z is hydrogen, a group represented by R as hereinbefore defined, or an amino substituted monovalent hydrocarbon group, at least one of the amino nitrogen atoms present in the group represented by the formula --R.sup.1 NZ.sub.2 having a hydrogen atom attached thereto; a is 1, 2 or 3 and has an average value of from about 1.8 to about 2.2; c is 1, 2 or 3, b is 0, 1 or 2; and the sum of (b+c) is never greater than 3 and has an average value of from 1.8 to about 2.2; and
(b) the reaction product of an organic polyisocyanate and a compound containing an alcoholic, phenolic, silanic or oximyl hydroxyl group or thiol group (hereinafter referred to as "blocked isocyanates") as a curing agent.
The Schank et al. compositions are highly stable and, upon curing by the reaction of the active hydrogen of the primary or secondary aminoorgano groups of (a) with the urethane or thiourethane groups of (b), are bondable and highly durable. However, the cured Schank et al. compositions can suffer from autogenous combustion, i.e., the cured compositions continue to burn after removal of an igniting flame. This problem renders the use of the cured Schank et al. compositions unacceptable for certain applications in which fire safety is important.
Schank et al. broadly discloses that fillers, thermal stabilizers and anti-oxidants are possible additional components in the Schank et al. compositions. Among the fillers disclosed by Schank et al. are zinc oxide and zirconium silicate. No specific thermal stabilizers or anti-oxidants are disclosed in Schank et al. There apparently is no prior art specifically disclosing the use of any specific combustion inhibiting additive to compositions cured by the mechanism involved in the cure of the Schank et al. compositions (i.e., the reaction of an amino nitrogen in a primary or secondary aminoorgano group of an aminoorganopolysiloxane with the urethane or thiourethane group of a blocked isocyanate). On the other hand, there is considerable prior art relating to the use of metal combustion inhibiting additives in organopolysiloxane elastomer compositions cured by other mechanisms. Such other curing mechanisms include curing by the action of free radicals generated by peroxides or the action of high energy electrons, curing through silicon-bonded vinyl groups, curing by the reaction of silicon-bonded vinyl groups with silicon-bonded hydrogen atoms, curing by the condensation of silicon-bonded hydroxy groups and silicon-bonded acyloxy groups, curing by the condensation of silicon-bonded hydrogen atoms and silicon-bonded hydroxy groups, and the like. The following is a description of the latter prior art.
U.S. Pat. No. 3,514,424 discloses flame-retardant, polydiorganosiloxane gum-based silicone elastomers prepared from compositions comprising an organosiloxane gum, a platinum compound and a non-alkaline filler which are cured with a peroxide or with high energy electrons. Gums containing aminoorgano groups and blocked isocyanate cross-linkers are not disclosed in this patent. This patent states that other generally equivalent noble metals, such as ruthenium, rhodium, iridium, palladium and osmonium, do not provide the desired flame retardance that platinum does for the compositions disclosed in this patent.
U.S. Pat. No. 3,734,881 discloses a self-extinguishing room temperature vulcanizable (RTV) silicone elastomer prepared from compositions comprising a hydroxy end-blocked polydimethylsiloxane, a silica or titanium dioxide filler, a platinum compound, a vinyl-containing silane cross-linking agent, and carbon black. Again, polysiloxanes containing aminoorgano groups and blocked isocyanate cross-linkers are not disclosed. This patent discloses that both platinum and carbon black are necessary for the RTV silicone elastomers to be self-extinguishing and that platinum alone does not provide self-extinguishing RTV elastomers. This patent additionally discloses that the presence of sulfur, tin, mercury, bismuth, or copper in the composition destroys the self-extinguishing properties of the silicone elastomer.
U.S. Pat. No. 3,821,140 discloses peroxide-cured, fire-resistant elastomers prepared from compositions comprising an organopolysiloxane rubber, an inorganic filler (e.g., titanium oxide), organic peroxide curing agents, and an additive comprising platinum and a rare earth metal oxide or rare earth metal hydroxide (the latter component optionally containing magnesium oxide). The patent discloses that conventional pigments such as chromium oxides and phthalacyanines and/or stabilizers such as iron, cerium and manganese octoates can optionally be introduced into the compositions.
U.S. Pat. No. 3,936,476 discloses silicone compositions comprising essentially (a) an organopolysiloxane; (b) finely divided silica filler; (c) finely divided manganese carbonate; and (d) platinum alone or in a platinum-containing compound. The compositions disclosed in this patent are cured utilizing organic peroxides or organohydrogenpolysiloxanes. This patent additionally discloses that the manganese carbonate in cooperation with the platinum or platinum-containing compound imparts excellent flame-retardant and self-extinguishing properties to the resulting silicone elactomers due to its function of generating CO.sub.2 gas under heat as well as its catalytic function. This patent further discloses that although calcium carbonate, zinc carbonate, cobalt carbonate, sodium carbonate can generate CO.sub.2 gas, these carbonates impart no improved self-extinguishing effects to the resulting elastomers and exert bad influences on the heat resistance of the elastomers.
U.S. Pat. No. 4,025,485 discloses fire-resistant compositions comprising an organopolysiloxane containing at least two silicon-bonded vinyl groups per molecule, an organohydrogenpolysiloxane containing at least three silicon-bonded hydrogen atoms, silica filler, zinc carbonate, ceric oxide and platinum.
U.S. Pat. No. 4,102,852 discloses a self-extinguishing room temperature vulcanizable (RTV) silicone rubber composition comprising an hydroxy end-blocked diorganopolysiloxane polymer, a filler (e.g., titanium dioxide or zirconium oxide), a metal oxide (e.g., zinc oxide), a trihydrocarbonoxy silane cross-linking agent, carbon black, platinum (solid or complexed) and a titanium chelate catalyst. This patent discloses that for optimum self-extinguishing compositions there should be 0.5 to 20 percent phenyl content and 0.01 to 10 percent vinyl content, based on the base diorganopolysiloxane. This patent also discloses that the addition of platinum compounds, disclosed in U.S. Pat. No. 3,514,424 as useful flame retardants for heat-cured silicone rubber compositions, does not markedly improve the flame retardance of RTV silicone rubber compositions.
U.S. Pat. No. 4,108,825 discloses that the addition of ceric hydrate to compositions containing vinyl-containing polydiorganosiloxane and organohydrogensiloxanes containing silicon-bonded hydrogen atoms when cured with a platinum-containing catalyst that is soluble in the vinyl-containing polydiorganosiloxane yield elastomers with improved flame retardance.
U.S. Pat. No. 4,405,425 dislcoses flame-retardant elastomers prepared from compositions comprising an organopolysiloxane, graphite and a metal hydroxide and/or a hydrate of a metal oxide such as alumina trihydrate, ceric hydroxide, cerous hydroxide, tricalcium aluminate hexahydrate and magnesium hydroxide. The compositions, depending on the storage stability, can be cross-linked by various means, including methylhydrogenpolysiloxanes and platinum catalysts.
In "The Influence of Platinum, Fillers and Cure on the Flammability of Peroxide Cured Silicone Rubber" [MacLaury, M. R., J. of FIRE & FLAMMABILITY, Vol. 10, 175 (July, 1979)], M. R. MacLaury (hereinafter referred to as "MacLaury"), in a detailed study of the action of platinum as a combustion inhibitor in organopolysiloxane compositions, concludes that the data present is consistent with the concept that free, uncured vinyl groups are important in flame retarding with platinum.
U.S. Pat. No. 3,137,670 discloses compositions comprising a diorganopolysiloxane and, as a heat stabilizer, a compound selected from the group consisting of manganese dioxide, nickelous hydroxide, nickelic oxide, chromic oxide, niobic oxide, cuprous oxide, cupric oxide, yttrium oxide, yttrium hydroxide and zirconium hydroxide. This patent discloses various curing agents useful with the composition including organic peroxides, hydrocarbonoxy silicates in the presence of metallic carboxylic acid catalysts, cellosolve silicates in the presence of metallic carboxylic acid salts and organohydrogensiloxanes. Compositions comprising aminoorganopolysiloxane polymers and blocked isocyanate cross-linking agents are not disclosed in this patent.
U.S. Pat. No. 4,404,305 discloses flame retardant translucent polyorganosiloxane resin compositions. In its discussion of the relevant prior art, this patent discloses that it is well known that the mechanism by which flame retardation is achieved varies with the particular compound and polymeric substrate, as do the adverse effects which flame retardants have on the physical properties of the substrate. This patent further discloses that flame retarding agents that have been proposed for use with elastomeric polysiloxanes include platinum and fumed titanium dioxide, optionally in combination with carbon black; platinum compounds in combination with conventional fillers; finely divided copper or copper compounds in a vinyl-containing polymer; powdered copper or copper compounds and various chlorinated organic compounds; and platinum compounds in combination with triphenyl phosphite. This patent then discloses a flame-retardant composition comprising a polyorganosiloxane resin, a halogenated organic compound and finely divided glass particles.
Thus, not ony does the prior art fail to disclose any specific metal combustion inhibiting additives for organosiloxane elastomer compositions which cure by the reaction of amino nitrogen with a urethane or a thiourethane, but even the prior art relating to the use of metal combustion inhibiting additives in organosiloxane elastomer compositions that cure by other mechanisms suggests that the effectiveness of metals for this purpose may be dependent upon the specific cure mechanism involved (see the MacLaury publication discussed above).
Accordingly, it is the object of this invention to provide heat-curable aminoorganopolysiloxane-blocked isocyanate compositions which have improved combustion resistance.